1. Field of the Invention
The invention relates generally to the production of dental porcelain restorations which are naturally appearing and relates particularly to dental restorations formed of layers of unique dental porcelains modified to internally handle light within said layers and to transmit back out of a restoration light of a value similar to the light which entered the restoration.
2. Description of the Prior Art
Dental restorations have been fabricated for centuries both for cosmetic and practical purposes. Within the last several hundred years, ceramic or porcelain powders have become the standard for forming such restorations. Reference is made to U.S. Pat. No. 3,400,097, the disclosure of which is incorporated hereinto by reference, which patent describes the use of porcelain powder by dentists and dental technicians for the build up and shaping of dental appliances such as crowns, bridges, artificial teeth and the like. These porcelain materials take the form of fine powders carried by a liquid binder which allow the formation of a "paste" such that a restoration can be built up and shaped to a desired tooth form. After shaping, the binder is typically removed such as by baking and the porcelain mass is sintered. Present conventional practice usually involves the formation of a porcelain dental restoration such as a crown or bridge on a metal framework which is called a "coping", the coping being covered conventionally by several layers of porcelain in an effort to simulate the appearance of natural teeth. A first layer of porcelain according to conventional practice is applied directly to the coping for the purpose of hiding the coping. This "opaque porcelain layer" is typically lacking any particular chromatic character. A second layer applied to the thus-coated coping is generally referred to as the "body porcelain layer" and exhibits a certain degree of translucence which is intended to be similar to that of the dentine layer of a natural tooth. Conventional practice further provides a third layer on top of the body porcelain layer, referred to as the "incisal porcelain layer", which is intended to approach the translucency of the enamel layer of a natural tooth. The various porcelain layers are typically baked between the layering steps. Pigments are typically provided in one or more of the layers referred to above to provide a color selected by a dental practitioner to be similar to that of the natural teeth or adjacent teeth or restorations present in the patient's mouth. A description of conventional restoration manufacture can be found in U.S. Pat. No. 4,828,117, the disclosure of which is incorporated hereinto by reference, this patent also providing a discussion of the formation of restorations on a ceramic base as well as on metal copings. The prior art has further provided porcelain dental restorations having fluorescing agents present in one or more porcelain layers. As an example, U.S. Pat. No. 4,645,455, the disclosure of which is incorporated hereinto by reference, describes the use of an ultraviolet fluorescing agent in the various layers of a porcelain restoration in an effort to match the appearance of a natural tooth under certain light conditions. Reference is also made to U.S. Pat. Nos. 3,880,662 and 4,645,454 which describe conventional dental porcelain powders, binders, baking and sintering processes, etc., it being understood that certain of the processes and materials described in these patents can be adapted for use according to the teachings of the present invention. For this reason, the disclosures of U.S. Pat. Nos. 3,880,662 and 4,645,454 are incorporated hereinto by reference.
Conventional practice in the art has heretofore produced somewhat less than satisfactory dental restorations. In fact, prior restorations, while adequate from the practical standpoint of use have failed to produce a warm, naturally appearing restoration which looks "life-like" or "alive". In essence, prior dental restorations including dental porcelain restorations, typically transmit gray or low value light back to an observer. The low value of light transmitted by prior dental porcelain restorations are caused in part by reflection of light off the metal surface of a coping, the light being reflected off the metal surface and going directly through the opaque layers and being thus transmitted by virtually direct reflection through the layers of the restoration. Further, prior dental porcelain restorations absorb high light values, particularly reds, yellows and oranges within the body of the restoration itself, the light being thus transmitted from the restoration being of a low value or a "gray" due to the absence of these absorbed light values. Accordingly, the present invention provides methods of making naturally appearing dental restorations, compositions of matter used in the practice of said methods and articles comprising dental porcelain restorations formed from the methods and compositions of matter, the present dental porcelain restorations being visually life-like due to the provisions of layers of dental porcelains which include pigments or chromas which cause internal handling of light in much the way light is handled internally of a natural tooth to provide an opalescent effect. Further, the present dental porcelain restorations include pigments or chromas which replace those light values, particularly the reds, yellows and oranges, which are typically absorbed by conventional dental porcelain restorations, the light thus transmitted from the present restorations being of a high value similar to light transmitted from a natural tooth. The present invention therefore provides substantial improvement in the art.